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TEC failure

Hi all,
I have a TEC wich is one of 12 controllers serving chilled water fan coil units with electric heat
All have common power supply and all on the same FLN
The TEC in question is showing failed points every morning and upon rest operates fine for the day. I have been able to determine the time of fault and every time it appears to be just before midnight when the scheduler shuts all the plant off for the night
It would appear from the outside the TEC is not returning from a power failure or FLN failure
Action so far:
Replaced TEC with brand new controller, readdressed set application, checked all settings against other controllers - still fails
Gave TEC its own power supply - still fails
seperateed FLN from other TEC and ran direct to MBC - still fails
Not sure what else to try - any suggestions

This was an existing fault. Upon taking the site over we had found a relay had been crudly wired in to reset the power supply to the controller. As above we started fresh. replaced the controller with new, re-addressed, etc etc

Does it fail if you disconnect the fln? Most likely you have a wiring issue with the fln or the temp sensor wiring. If you have faulty wiring between the room temp sensor and the tec it can cause problems similar to faulty fln wiring. Make sure you don't have duplicate addresses on the fln also. Seems strange that it happens at the same time though.

You can simulate the same failure if you disconenct the FLN or power supply. I have checked the temp sensor and wiring and appears ok, however a sensor fail or wiring fail would most likly be at random times not at shutdown. Have double and tripple checked the addresses

All the AHU's start and stop at the same time with about one minute intervals between. With the one power supply to all TEC's, even if there was a brown out wouldnt/shouldnt they all reinitiate.

I have seen similar problems before and it usually turns out to be a wiring issue. Check the Aux temp sensor. I've seen temp sensors wires pinched between the j-box and cover cause some weird problems. One of the TECs having the FLN wire polarity reversed can cause random failures on the FLN. Check the wires to the valve and electric heat.
You mention that you have 12 TECs on one power supply. That's too many for a single 100VA power supply. Probably not the problem though since you tried a separate power supply.
Try using a different address. Disconnect the TEC from the FLN, readdress with a different address, delete the old address from the system profile, add a new TEC to the system profile with the new address, reconnect the TEC to the FLN. I have found that sometimes a corrupt database can be the problem and the best way to fix it is to delete and start over.